Alternatives for
Small Wastewater
Treatment Systems
Cost/Effectiveness Analysis
EPA Technology Transfer Seminar Publication
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EPA-625/4-77-011
ALTERNATIVES FOR
SMALL WASTEWATER SYSTEMS
Cost/Effectiveness Analysis
ENVIRONMENTAL PROTECTION AGENCY* Technology Transfer
October 1977
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ACKNOWLEDGMENTS
This seminar publication contains materials prepared for the U.S.
Environmental Protection Agency Technology Transfer Program and
presented at'the Technology Transfer design seminars throughout the
United States.
The information in this publication was prepared by J. J. Troyan,
Project Manager, and D. P. Norris, Vice President, of Brown and Cald-
well, Consulting Engineers, in Eugene, Oreg.
NOTICE
The mention of trade names or commercial products in this publication is for
illustration purposes, and does not constitute endorsement or recommendation for
use by the U.S. Environmental Protection Agency.
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,i
CONTENTS
Chapter I. Evaluating Alternative Wastewater Systems for Municipalities
Problem Conditions
Description of Alternatives in Cost/Effectiveness Analysis
Procedures for Evaluating Alternatives. . .
Chapter II. Case Histories
Glide-Idleyld Park
Bellevue
Westboro
Fountain Run . . .
East Ryegate ....
1
1
4
7
13
13
17
20
23
27
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Chapter I
EVALUATING | ALTERNATIVE
WASTEWATER SYSTEMS FOR MUNICIPALITIES
In response to the increasingly acute financiE 1 problems presented to small communities and
rural residential areas in the past 5 years resulting
from pollution control requirements, new empha-
sis is being placed on examining the possible use ox nonconventional sewerage systems. The mere
proposal of conventional community systems, because of the magnitude of the cost to individual
homeowners living in these areas, has quite often only served to delay taking any kind of'action.
For many years, research and development work has been accomplished on individual on-site treat-
ment and disposal systems and on nonconventional systems (for example, pressure sewers). Never-
theless, the most recent work, initiated because oi the high cost of the conventional systems, has
only begun to become familiar to consulting engir eers and public officials in the wastewater man-
agement field.
The objective of this publication is to presen
; specific information pertinent to the cost/effec-
tiveness analysis of sewerage systems for small communities and rural residential areas. Toward that
end, procedures for use in determining the feasibility and desirability of using four on-site systems
and four types of community collection systems nave been included. The material herein does not
emphasize procedures for the selection of commu lity treatment systems.
The publication, in particular, includes sectic ns describing the problem conditions that must
be considered in selecting sewerage alternatives. It will also point out the advantages, disadvantages,
and limitations of several on-site and community collection alternatives, a procedure for screening
and analyzing costs of alternatives for individual nomes, and a set of case histories taken from
recent sewerage reports and facilities plans that show how and why some of the more nonconven-
tional systems have been analyzed.
PROBLEM CONDITIONS
To evaluate on-site sewage disposal systems 2 nd nonconventional community collection sys-
tems, three basic premises should be borne in min I.
If site conditions are suitable, the convi
ntional septic tank-soil absorption system
(ST-SAS) is the best type of on-site disposal system.
If costs are reasonable, a conventional gravity sewage collection system is the best type of
community system.
A conventional gravity collection system is the accepted standard for community sanita-
tion against which all alternatives should be measured.
It is recognized that there are
situations in wni
ich the conventional ST-SAS would not work
satisfactorily, and in which the cost of a conventional gravity system would be exorbitant. The
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problem is one of sorting out the alternatives in a rational manner and selecting a short list of alter-
natives that warrant .detailed analysis. Fortunately, recent work in the area of alternative collection,
treatment, and disposal systems for small flows has provided a background of information, which
makes possible the initial screening of alternatives with a minimum of time and a high level of con-
fidence. The screening process is effective because there is a range of available alternatives, each of
which deals with certain specific problem conditions and each of which may be most cost/effective
in a certain rather narrow set of circumstances. The starting point for the screening process, there-
fore, should be an inventory of the problem conditions encountered in the study area. The principal
problem conditions may be grouped into four categories: soils, site characteristics, geology-
hydrology, and climate.
Soils
Quite naturally, the nature of the surface soils has a major effect on the function of SAS's.
There are three factors that are of particular concern.
Permeability. It is a well-recognized fact that SAS's will not work in soils that will not absorb
water. Tight clays and other soils of low permeability as a rule preclude the consideration of SAS's.
Often 60 min/in as measured by the percolation test is used as the lower limit of permeability for
SAS's, but the authors believe this value to be unnecessarily restrictive,, especially in light of the
accuracy of the test. In a well-designed and properly constructed ST-SAS, a percolation rate of 120
min/in can be more than adequate to support the rate of infiltration from the disposal trench into
the adjacent soil. Soils of very low permeability will also usually preclude the use of percolation-
assisted evapotranspiration (ET) systems.
Depth to Impermeable Layer. Even though surface soils.may have adequate permeability, an
SAS will not work if a shallow impermeable layer prevents downward percolation of the waste-
water. A shallow impermeable layer may lead to an accumulation of perched water that will flood
the disposal trench and cause clogging of the trench infiltrative surface. An unsaturated soil column
of about 3 feet is generally accepted as adequate for effective draining of fine-grained soils.
Depth to Creviced Bedrock. Experience has shown that unsaturated soil is an excellent
medium for the removal of pathogenic bacteria and viruses. Wastewater, however, may flow for
long distances through crevices in bedrock without such purification. One goal of an adequate SAS,
therefore, is to achieve an adequate distance of travel through unsaturated soil before the waste-
water enters crevices in underlying bedrock. A commonly accepted value for the minimum depth of
unsaturated soil is 2 to 3 feet for fine-grained soils and up to 10 feet for coarser soils.1
Site Characteristics
Lot size and study area topography influence the selection of available alternatives for waste-
water disposal.
Lot Size. The average lot size and corollary factor of distance between homesites influence the
feasibility of both on-site and community sewerage systems. For example, a minimum lot size of
about 1 acre is frequently required to accommodate an adequate ST-SAS with proper allowances
for setbacks and for the house itself. It is not normally desirable to construct any subsurface dis-
charge system on lots smaller than one-half acre. If water is obtained from individual wells, the
minimum lot size should be about 1 acre.2
The cost of conventional community sewerage, on the other hand, increases rapidly as the
distance between households increases and population decreases. For average lot sizes of 2 acres or
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more, community sewerage is not ordinarily the
one-half and 2 acres, particularly where the ST-!
may be required to select the most cost/effective
r lost economical solution. For lot sizes between
SAS is not a suitable solution, a careful cost analysis
method of wastewater management.
Topography. Although an adequate slope is necessary for gravity sewerage, excessively steep or
irregular topography can limit the options available. A slope of about 25 percent is usually consid-
ered limiting for an ST-SAS, and construction of any on-site system is difficult at that slope. Irreg-
ular, hilly topography frequently requires numerous lift stations if a gravity collection system is
installed. This is more likely to be true if the area
was developed entirely on septic tanks, and roads
a shift in the economics in favor of a community
were laid out without thought of later construction of sewers. Under these conditions, there is often
jressure sewer system. Vacuum sewers are not
well suited for use in irregular, hilly topography, b1 ut may offer some cost advantage should there be
no slope. This would be particularly true if soils a'e unstable.
Geology and Hydrology
Depth to bedrock, soil stability, and ground
group of factors involved in the selection of the
which rules out the use of the ST-SAS. Bedrock c
water hydrology are probably the most important
system for a small wastewater flow.
b;st
Shallow Bedrock. Bedrock within 5 feet of tie ground surface forms an impervious layer,
oser than 6 feet to the ground surface will prob-
ably result in excessive costs for any gravity collection system. Closer than 3 feet to the surface,
bedrock probably rules out most on-site systems, except septic tank/slow sand filter/surface dis-
charge systems, mound systems, or, in some casesl ET systems. Only pressure or vacuum collection
systems are likely to provide community sewerage at a reasonable cost in an area with shallow bed-
rock.
Unstable Soils. Common examples of soil instability are sandy soils with a high water table,
and fine sediments with a high water content such as those found in swamps and some tidal estu-
aries. Costs of dewatering, sheeting, and other measures necessary to construct deep sewers in un-
stable soils may cause a fivefold or greater increase in sewer construction cost. Some types of
unstable soils can cause gravity sewer lines to shift after they are installed, changing slopes and add-
ing high maintenance costs to high construction cost.
Seasonal High Ground Water Within 4 Feet of Surface. There is abundant documentation in
the technical literature for the fact that high ground water has a detrimental effect on the function
of an ST-SAS. Inundation of the infiltrative surface because of seasonal high ground water or perch-
ed water on top of an impervious layer leads to rapid failure of the SAS, which can be reversed only
by an extended rest period. A commonly used limiting value for seasonal high ground water in fine-.
grained soils is 3 feet below the bottom of the drainfield trench. For coarser, granular soils a lower
value may be acceptable. For a minimum-depth dcainfield trench of 12 inches of gravel-fill with the
top of gravel at-natural ground surface and covered by a mounded soil-fill about 12 inches deep for
protection, the limiting minimum depth to seasor al high ground water is about 4 feet. For higher
ground water levels, a modified, mounded SAS must be used to raise the infiltrative surface above
natural ground level.
Seasonal High Ground Water Within 24 Inches of Surface. Even with the use of a mounded
system there is a limit to the acceptable ground water height. Water that flows downward from a
mounded SAS must be able to flow laterally from under the mound into the adjacent soil mantle
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without surfacing at the edge of the mound. To prevent surfacing at the edge of the mound, the
ground water beneath the mounded system should not rise to within 24 inches of the surface for
any extended time period (the equivalent of 2 weeks or more). The seasonal maximum ground
water height can be assumed to be an upper limit on any type of SAS.
Climate
Except for the special conditions that prevail in arctic climates, climatic factors have little
effect on most community sewerage systems. Climate can, however, be severely limiting for certain
on-site disposal systems.
Long, Cold Winters. Extended periods of severe cold will preclude the use of uncovered sand
filters because of ice formation on the filter surface. A long, cold winter will as a rule limit annual
ET to the point that ET units will not function properly.
Low Net Annual ET. Even in warm climates, excessive rainfall may limit ET to a value that
will preclude the use of ET systems. Quite obviously, a unit relying solely on ET will not function
in an area where the net ET is zero or negative. Units have been designed for combined ET and per-
colation rates ranging from 0.15 to 1.6 in/d.3 As a practical matter, ET units should be evaluated
very carefully in any location where the net annual ET is 24 inches or less. For a suburban family of
five with a per capita water use of 100 gal/d, for example, a 24-inch net annual ET would require
more than one-quarter acre to construct an adequate ET bed.
DESCRIPTION OF ALTERNATIVES
IN COST/EFFECTIVENESS ANALYSIS
Eight separate alternatives for disposal of wastewater from individual homesites, listed in table
1-1, are described briefly in tables 1-2 and 1-3. The alternatives are divided into two groups: on-site
systems (table 1-2) and community collection systems (table 1-3). Each alternative included in the
description and in the following screening process depends to some extent on the problem condi-
tions described in the preceding section. Community treatment systems are not described, because
only their cost, and not their use, depends on the specified problem conditions. In addition, because
collection system costs are usually predominant in the total cost of a new sewerage system for a
small community, the basic choice in a cost/effective analysis will ordinarily be between on-site
systems and community sewers of one kind or another.
The alternatives are described in terms of the advantages, disadvantages, and limitations of
each. Limitations listed for an alternative are those characteristics that would prevent the use of the
alternative. Advantages and disadvantages are characteristics that determine the relative desirability
of the alternative but do not bear directly on whether or not it can be used.
Table 1-1 .—Alternatives in cost/effectiveness analysis
Group
Alternatives
A. On-site disposal systems
B. Community collection systems
ST-SAS
ST-Mound
ST-ET/ETA
ST/sand filter/surface discharge
Conventional gravity sewers
Small-diameter gravity sewers
Pressure sewers
Vacuum sewers
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PROCEDURES FOR EVALUATING ALTERNATIVES
The evaluation of alternatives for on-site syst ;ms and small community systems should begin
with the basic assumption of equality in system life and performance. It makes little sense, for ex-
ample, to compare a system of unquestioned reliability with a system that may be inoperative sev-
eral weeks in the year. Similarly, a system having in anticipated life of 40 years should not be com-
pared with a system with an anticipated life of 10 years unless allowance is made for fourfold re-
placement of the latter. Starting with this basic assumption of equality of service, the first step in
evaluation should be a screening process to select the most suitable alternatives. The selected alter-
natives should then be compared in terms of life-cycle costs, and the length of the selected life cycle
should be at least equal to the projected life of the structures that the system is designed to serve.
Screening of Alternatives
For practical application, there are two aspecjts to the determination of feasibility of alter-
natives: technical feasibility and administrative feasibility.
Technical Feasibility. Each of the problem conditions described earlier limits in some respect
the application of certain sewerage alternatives. For each problem there is a probable best response
in terms of selecting or discarding sewerage alternatives. Note the qualifying word "probable."
There are, of course, varying combinations and degrees of problem conditions, which render any
absolute judgment impractical. With this qualification, however, the available alternatives may be
screened for technical feasibility in accordance with table 1-4.
Administrative Feasibility. As a practical mat
;er, no sewerage alternative is feasible unless its
construction is approved by appropriate regulatory agencies. A mounded SAS may be the best solu-
tion to a particular problem, but if present regulations forbid its use, it is not a feasible alternative.
That is not to say that modification and improvement of existing regulations should not be at-
tempted, but that each decision must be made'with.in the context of the regulations in effect at the
time.
An example is the use of an on-site sand filter
Research indicates that sand filtration of septic tank effluent, followed by chlorination and direct
discharge to surface waters, is an acceptable indivic
tions, however, such a unit would usually require a
followed by direct discharge to a waterway.
.ual on-site disposal system. Under current regula-
specific National Pollutant Discharge Elimina-
tion System (NPDES) permit, and the system would possibly be discarded as administratively un-
workable. The final step in screening alternatives, therefore, is the discard of those technically feas-
ible solutions that cannot be implemented within tjhe framework of existing regulations.
.ve screening process, must be alert to catch
ot permitted and those that are permitted but
latter case, regulations governing ST-SAS's in
•e not recognized as substandard. A cost com-
•age systems under such circumstances will vio-
hich all alternative systems should be com-
The engineer, in the course of the administral
those alternatives that are technically feasible but
are not technically feasible. As an illustration of tl
many areas permit the installation of systems that
parison of septic tank systems and community se1
late the basic assumption of equality of service on
pared.
Cost Analyses
It is not the intent of this paper to set forth specific unit costs that should be used in evaluat-
ing alternatives for small community or on-site wastewater systems. The costs may vary significantly
from community to community, and any professional engineer can prepare a more accurate cost
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Table 1-4.—Technical screening of alternatives
Problem condition
Probable best response
Soils:
Impermeable
Shallow permeable layer over impermeable layer or
creviced bedrock
Site:
Average net lot size 2 acres or more .
Average net lot size less than 1/2 acre
Steep slopes
Irregular, hilly topography that would require deep
cuts or numerous lift stations
Geology-hydrology:
Shallow bedrock
Unstable soils which result in high excavation costs
Seasonal high ground water within 4 feet of surface
Seasonal high ground water within 2 feet of surface
Climate:
Long, cold winters
Low net annual ET
Discard ST-SAS, ST-Mound, and ST-ETA
Discard ST-SAS and ST-ETA
Discard conventional gravity system
Discard ST-SAS, ST-Mound, ST-ET, and
ST-ETA
Discard ST-SAS and ST-Mound
Discard conventional gravity collection system,
small-pipe gravity system, and vacuum
system
Discard ST-SAS, ST-ETA, and both conventional
and small-pipe gravity collection systems
Discard conventional and small-pipe gravity
collection systems
Discard ST-SAS
Discard ST-Mound and ST-ETA
Discard ST-ET
Discard ST-ET
aSeptic tank with conventional soil absorption system. Septic tank with mounded soil absorption system. Septic tank with
evapotranspiration-soil absorption system. Septic tank with evapotranspiration system.
comparison from local information than could be presented here. Rather, the purpose is to point out
the fundamental alternatives in terms of equal life-cycle performance.
Any on-site system should be evaluated over a period equivalent to the life of the structure it
serves. For a single-family dwelling, a reasonable life is 50 years, and all cost comparisons that in-
clude on-site systems should be compared over that period. To do otherwise is unrealistic. If a con-
ventional ST-SAS is known to have a short life span in an area, it is not relevant that it may be the
apparent best solution based on present capital costs. The owner in 10 years may be faced with the
cost of an expensive sewerage project required for the protection of public health. In extreme cases,
failure to plan a sewage disposal system for the life of the dwelling has resulted in people being
forced to abandon their homes to avoid a serious health hazard. A utility function should not be
allowed to govern the useful life of the dwelling. Furthermore, insofar as possible, the most eco-
nomical system should be selected to serve the life of the dwelling.
The cost analysis, for community sewerage systems and for on-site systems, must include all
reasonable operating and maintenance costs associated with the systems. Moreover, where appro-
priate, the cost of establishing and operating public agencies to supervise construction, operation,
and maintenance of the systems should be formulated.
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Costs for Septic Tanks. Each system that incorporates a septic tank should include an evalua-
tion of other pertinent costs, as follows:
• The cost of an initial construction permit (the permit will also cover the effluent disposal
system)
Initial cost of the septic tank installed
Cost of pumping the septic tank at intervals
If the tank is steel, the cost of replacembnt
almost directly with the amount of infiltrative SUE
required by regulation varies widely from State to
some common basis is necessary for the calculation of life-cycle costs that can be reasonably com-
pared with the cost of other alternatives. The lack
agreement in the scientific community with respect to the basis for design of the infiltrative surface
area. McGaughey, Krone, and Winneberger3 recommended consideration of only the sidewall area
of the disposal trench. Bouma,4 on the other hand
not greater than once every 4 years
at 15-year intervals
intervals no greater than 2 years (the inspection will
The fee for a periodic inspection at i
also cover the effluent disposal system)
Costs for SAS's. The cost of an SAS, either subsurface or mounded, may be assumed to vary
lace area provided. As the infiltrative surface area
State, and in many cases from county to county,
of uniformity in regulations is matched by dis-
, recommends consideration of only the bottom
area of the disposal trench. Healy and Laak recommend use of both the sidewall and bottom area of
the disposal trench as a useful infiltrative surface area.5 For the disposal trench configurations most
commonly required by regulations, sidewall area is
about equal to bottom area, and probably either
can be used. In any case, the most important factor in the design of an SAS is the provision of suf-
ficient infiltrative surface, and a current conservative approach would therefore use either sidewall
area or bottom area, but not total trench area.
The life of the individual SAS's will vary for any given design, depending on the site charac-
teristics, household water use, and attention to septic tank pumping. Some systems will fail early
and some will last indefinitely. SAS's should be evaluated to determine if they will, on the average,
provide a level of environmental sanitation equivalent to that obtainable from conventional gravity
sewerage systems. One way to approach such an evaluation is to define a "median" or "control"
system that can be expected to last 15 years, on the average, before failure. Using a control system
as a basis for comparison, any set of regulations may be used to compare septic tanks in an area
assuming the following:
« The life of a properly installed SAS is directly proportional to the amount of infiltrative
surface area, provided that the soil percolative capacity is above a limiting value.
» A gravity-dosed absorption system in fine-grained soils, having 450 ft2 of infiltrative sur-
face area to each bedroom, is defined as a control system. It will last for 15 years. A pro-
portionately shorter life will result from! a system having an infiltrative surface area with a
lower ratio.
An SAS, supplemented after failure with
valve, may thereafter be operated by alt
of the dwelling.
a second identical system and an alternating
amately resting each half. It will last for the life
Systems having a ratio below that of a
shorter intervals until the total installed
c >ntrol system will have to be supplemented at
infiltrative surface equals that of two control
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systems. Thereafter, the systems may be rested alternately, and they will last for the life
of the dwelling.
• Coarse-grained soils that permit clogging in depth at the infiltrative surface will accept
higher application rates.5 <6 It is assumed that a control system for coarse-grained soils
may be defined as 250 ft2 of infiltrative surface area to each bedroom.
The cost evaluation for SAS's, based on the foregoing assumptions, should include the follow-
ing items:
• Initial construction cost of the absorption system
« Cost of constructing a supplementary absorption system in accordance with the foregoing
assumptions on design life
• For systems in which the septic tank effluent is pumped to the disposal field:
— Initial cost of installing the pumping unit, complete with electric power and controls
^
— Cost of replacing the pumping unit every 10 years for the life of the dwelling
— Cost of power and maintenance for the pumping unit (maintenance cost should in-
clude at least one service call each year)
Costs for ET Systems. Each ET system must be preceded by a septic tank, with cost estimates
as set forth in the foregoing paragraph. A very careful cost comparison should be made wherever
septic tank-evapotranspiration-soil absorption system (ST-ETA) units are considered to be certain
that ST-SAS units are not more cost/effective.
ET units may be expected to work in favorable climates where impermeable soils or high
ground water prevents the use of SAS units. Lined beds are usually required in areas with high
ground water. To date very limited information is available for use in developing a reliable predic-
tion of the average life of ET units, but for the purposes of this discussion it is assumed that prob-
lems with salt buildup and bed linings will require complete bed replacement every 15 years. This
criterion is assumed in lieu of more definitive information.
Costs for Sand Filters. A sand filter is subject to the same limitations on its useful life as an
SAS. Unattended, its infiltrative surface will eventually clog, and it must be renewed periodically by
scraping and replenishment of the sand. The filter structure may be expected to last indefinitely as
long as it is adequately maintained. Sand filtration and direct discharge are assumed to include efflu-
ent disinfection. This is a high-maintenance system that the individual homeowner cannot be ex-
pected to maintain, and its use, even where permitted by regulatory agencies, should be supervised
by a qualified public agency. A cost evaluation of sand filter systems should include the following:
• Initial construction cost that would include fencing for mild climates and a complete
cover for severe climates
• Bimonthly inspection of the disinfection equipment and replenishment of chemicals, if
required
• Cost of power and chemicals for disinfection
• Semiannual rejuvenation of the sand surface
10
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Replacement of the chemical feed equipment every 10 years
All costs for septic tanks as set forth
earlier
« If pumping to the filter is required, all costs for pumping as described for SAS's
Community Systems. The elements of community collection and treatment systems are well
known; the costs therefore need little explanation. Nonetheless, in comparing a community system
with individual on-site systems, it is important that the comparison be made over a time period that
represents the life of the dwelling, and that it ir elude all costs to the individual homeowner. The
comparison should include the following costs:
• The installed cost of the community system, recognizing that the elements of a commun-
ity collection system, except for mec lanical equipment, ordinarily have a life expectancy
of 50 years
• The installed cost of all on-site components of the community system, such as house con-
nections and septic tanks, where required '
• For pressure systems and small-pipe gravity systems, all of the costs associated with septic
tanks as listed in an earlier paragraph
Summary
It is believed that the foregoing procedures
and maximum uniformity the most suitable alternative
The procedures allow for variations in local regi lat:
the basis of equality of function over the life of
for evaluation will identify with a minimum effort
for handling small community sewage flows.
ions and permit consideration of alternatives on
the system.
REFERENCES
1J. C. Romero, "The Movement of Bacteri
Water, 8, 2, Mar. 1970.
2 J. A. Cotteral and D. P. Norris, "Septic T;
Eng. Div., 95, SA-4, Aug. 1969.
i and Viruses through Porous Media," Ground
ink Systems," Proc. Am. Soc. Civ. Eng. J. Sanit.
P. H. McGaughey, R. B. Krone, and J. H. Winneberger, "Soil Mantle as a Wastewater Treat-
ment System," Sanitary Engineering Research Laboratory Report No. 66-7, University of Califor-
nia, Berkeley, Sept. 1966.
4 J. Bouma, "Unsaturated Flow During Soil
Soc. Civ. Eng. J. Sanit. Eng. Div., Dec. 1975.
1974.
5K. H. Healy and R. Laak, "Problems with
6 P. H. McGaughey and J. H. Winneberger,'
Treatment of Septic Tank Effluent," Proc. Am.
Effluent Seepage," Water and Sewage Works, Oct.
Final Report on a Study of Methods of Preventing
Failure of Septic Tank Percolation Systems," Pr6c. Am. Soc. Civ. Eng. J. Sanit. Eng. Div., Report
No. 65-17, University of California, Berkeley, Oclt. 1965.
11
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Chabfer II
CASE HiSTORIES
Chapter I described problem conditions thlat should be considered in analyzing wastewater
systems for small communities, alternative systems that might be used as tools to overcome particu-
lar problems, and a recommended procedure fo:: ascertaining which system or systems would be
best suited for any one of a number of conditio as. A set of five case histories drawn from recent
facilities plans are next presented to show why and how relatively innovative and nonconventional
wastewater systems have been developed, analyzed, and in some cases selected as the most cost/
effective solution to a sewerage problem in a small community. Although not all alternatives de-
scribed earlier in this paper are represented in the case histories, they do provide an overview of
responses to small-community sewerage problems. The case histories do not represent examples of
the proposed cost-analysis procedure described in the preceding section but are included as sources
of information and knowledge. They were discussed in the Technology Transfer municipal design
seminars for small wastewater treatment syster
GLIDE-IDLEYLD PARK
Glide-Idleyld Park is an unincorporated community in Douglas County, Oreg., with a present
population of about 2,500. The area is without public sewers at present, and all wastewater is
treated in septic tanks and disposed of through drainfields. Numerous drainfield failures have
occurred, however, because of unsuitable soils and high ground water conditions. As a result of the
problem, the Douglas County Department of Public Works undertook a study of wastewater man-
agement for the area in 1975. The material for tjhe case history is taken from that study.1
Physical Characteristics
Glide-Idleyld Park is located in a scenic set ;ing along the North Umpqua River on a highway
leading to Crater Lake National Park. The area is noted for fine trout fishing and scenic beauty.
There has also been increased interest in recent years in home building in the area. The sewerage
study revealed the following information with respect to the physical characteristics of the area.
Climate. The region has a temperate climat
winters.
Spils and Geology. Claylike soils are found
rock occur near the surface in some areas.
; with moderately warm summers and wet but mild
throughout the study area, but outcroppings of
Ground Water. High ground water is prevalent throughout the study region. Although abun-
dant evidence of surface water pollution was presented in the report, the extent of ground water
pollution as a result of failing drainfields was unknown.
Topography. The physical features of the
many visitors to the area. The terrain varies fron
with solid rock in many places.
s;;udy
area are widely varied, which appeals to the
gently rolling fields to steeply sloping hillsides
13
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Site Characteristics. The total study area contains approximately 13,000 acres, is 11 miles in
length, and averages 1.75 miles in width. At present, most of central Glide is divided into lots rang-
ing from 20,000 ft2 to 1 or 2 acres. Many of the lots do not lend themselves to subdivision. Present
low-density residential areas have a preponderance of 1-acre to 7-acre parcels, few of which could be
subdivided. Densities used for future planning were 1 acre for 1.5 homes for the more urban por-
tions of the study area, and 2 acres for a home in the outlying areas.
Alternatives and Screening Process
Although no screening process is explicitly presented in the sewerage study, the following facts
provide a basis for detailed analysis of the alternatives.
• Of the existing ST-SAS units, 60 percent are failing.
• Analysis of soils in the area showed that a very limited portion was suitable for installa-
tion of drainfields because of the predominance of claylike and rocky soils. In some areas,
shallow surface soils overlie basalt bedrock.
• Three previous studies of the area had recommended community sewerage. The suggested
design was conventional gravity sewers.
• Public response in surveys and at public meetings indicated that almost 80 percent of the
residents favored installation of sanitary sewers.
• Cost had prohibited action on any of the initial three sewerage plans.
• In 1974 the County Engineer's Office had conducted a study of pressure sewers. The
report contains the following paragraph in the opening discussion: "Though there are
similar systems, such as vacuum sewers, or wastewater quantity reduction by reuse of
'grey water,' it is believed pressure sewers hold the most promise in difficult terrain and
where a number of homes are of concern."2
As a result of the foregoing factors, the cost/effectiveness analysis in the sewerage study ex-
amined two methods of wastewater collection: pressure sewers and conventional gravity sewers. In
addition, two types of treatment were considered, both disposing of final effluent by discharge to
the North Umpqua River during the winter and by land application during the low-flow summer
months.
Cost/Effectiveness Analysis
An analysis of cost/effectiveness of alternatives for community sewerage in Glide-Idleyld Park
included the collection system and the treatment and disposal system. Emphasis in the study was
given to the collection system, as it had been the most expensive item in previous studies.
Collection System. Construction costs and operation and maintenance costs are presented in
the Douglas County report in terms of present worth.
Unit construction costs for the conventional collection system alternative were obtained from
county, State, and Federal data, and information from two consulting engineering firms. Operation
and maintenance costs were obtained from local sewerage agencies in terms of dollars per mile of
line and dollars per person served. A detailed analysis of the required lengths and sizes of the con-
ventional system components was conducted that include estimates of the segments of force main
and the amounts of rock excavation needed. The resulting costs of the conventional system are
shown in table II-l.
14
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Table 11-1 .—Cost of conventional collection system, Glide-ldleyld
[D
ollars]
Component
x' Total •
Present worth3
Construction
2,523,400
424,400
169,000
515,200
772,000
4,404,000
Operation
and
maintenance
104,900
38,700
0
0
118,000
261,600
Total
2,628,300
463,100
169,000
515,200
890,000
4,665,600
aRounded to nearest $100 and calculated using 5.875 percen
: interest over a 20-year design period.
Unit construction costs for the pressure sew er collection system alternative were more difficult
to obtain. The county gathered the costs from national suppliers of materials and local contractors
to get the best possible data on labor and equipment needs for installing pipelines, pumps, septic
tanks, and electrical instrumentation. The service connection at each home was laid out to include
pumping of septic tank effluent from a small we| well to the local pressure collection sewer. In the
design, 612 existing homes and small businesses were to be served by 568 pumps at an overall aver-
age cost of $1,155 per connection, excluding treatment and collection system costs. Operation and
maintenance costs were obtained from agencies throughout the United States currently using pres-
sure sewer systems, from suppliers of effluent pumps in Oregon, and from the local water supply
agency. In terms of 1975 prices, each pumping unit was estimated to require $50 per year in main-
tenance, and the pipelines were estimated to cos; $100 per mi/yr. The resulting costs for the pres-
sure sewer collection systems are shown in table II-2.
A comparison of tables II-l and II-2 shows
system is almost exactly one-half the cost of the
$2.3 million. As expected, operation and
than for the conventional system. The costs are
initial cost of the pressure system is only 44
amounting to a savings of almost $2.5 million.
that the total present worth of the pressure sewer
conventional collection system, a difference of
maintenance costs for the pressure sewer system are higher
more than 60 percent, or $166,000 higher, but the
percent of the initial cost of the conventional system,
Treatment Plant. Inasmuch as treatment and reuse.of effluent is not feasible in the Glide area
and insufficient land is available to rely on land application as a year-round disposal method, treat-
ment and river discharge with summer land application was chosen as the only practical alternative.
Two methods of treatment were considered: extended aeration with effluent polishing by micro-
straining and aerated lagoons followed by interniittent sand filtration. As noted in the report, "The
extended aeration option is common in Oregon and found to be generally acceptable. Lagoons,
however, have not been generally accepted due to poor effluent quality." As no intermittent sand
filters were in operation in Oregon at the time the study was being conducted, it was not known if
the State Department of Environmental Quality would accept such a recommendation. Therefore,
for the purposes of the study, extended aeration and microstraining were used for determination of
user charges for a complete project. At the same time, the county stated its intention to continue
evaluation of the cheaper lagoon-sand filtration alternative. Comparative costs for the two treat-
ment systems are shown in table II-3.
15
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User Charges
An assessment of user charges for the recommended project—collection by pressure sewers and
treatment by extended aeration, microstraining, and summer land application—was also made. Com-
ponents for the initial cost and the operation and maintenance costs for a single-family residence are
shown in table II-4.
Table \\-2.-Costofpressuresewersystem, Glide-ldleyld
[Dollars]
Component
Pressure mains
Service connections
Rock excavation
Mainline pump stations
Total . . .
Present worth3
Construction
900,900
853,700
126,000
76,000
1,956,600
Operation
and
maintenance
28,900
374,300b
0
24,700
427,900
Total
929,800
1,228,000
126,000
100,700
2,384,500
BRounded to nearest $100 and calculated using 5.875 percent interest over a 20-year design period.
"Includes both initial and future connections.
Table \\-3.-Comparison of glide area treatment costs
'[Dollars]
Process3
Extended aeration plus microstraining
Stabilization ponds plus intermittent sand filtration
Construction
cost
350 000
150000
Annual operation
and maintenance
cost
?8000
5000
aEach facility sized for a 0.3 mgd design capacity.
Table 11-4.—User charges for a single-family dwelling, Glide-ldleyld
[Dollars]
Item charged
Initial assessment for system cost and lot hookup3
Annual charge for initial assessment at 6 percent interest over
20 years '. . .
Annual operation and maintenance charges
Total annual charge to initial singlefamily users
Initial cost
1,500
Annual cost
129
114
243
"Assessments for future hookups were estimated to be $1,800, or $300 more than for initial users.
"An annual charge for septic tank pumping is included in the annual operation and maintenance charge, based on local rate of
$35 for pumping a single tank.
16
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Bellevue is a community of approximately
case history presents a cost/effectiveness analysis
individual subsurface disposal systems or installing
The description and analysis are taken from a
BELLEVUE
550
Physical Characteristics
The physical characteristics described in the
water hydrology and quality, topography, and site
persons located in south-central Idaho. The
o|f the alternatives of either continuing the use of
conventional gravity sewers in the community.
facilities plan prepared for Elaine County, Idaho.3
leport include climate, soils and geology, ground
characteristics.
Climate. At an elevation of 5,200 feet, Bellevue has a long winter and a short, rather cool sum-
mer. The mean annual snowfall is approximately 100 inches, most of which falls between November
and March. Mean daily minimum temperatures are usually below freezing from September through
May.
Soils and Geology. As part of an ancient lakebed, the ground beneath Bellevue is composed of
alternating layers of clay, sand, silt, and gravel. The soil in the vicinity of the community is charac-
terized principally as a well-drained, shallow, gravelly loam. It has been described by the Soil Con-
servation Service as poor for subsurface disposal because of its coarse texture, creating a consider-
able possibility of ground water contamination.
Ground Water. Depth to ground water in anc
feet. Ground water quality is excellent above and
mestic and agricultural uses. Samples taken below
around the community is as a rule more than 25
below Bellevue and is currently suitable for do-
Bellevue, particularly with respect to the direc-
mestic anci agricultural uses, oampies tan-eu uciuw UCU.CVIAC, ^cu.ujn-^u^i-ij' mu** ^.^^^^^^ „« ~~~ ™
tion of ground water flow, show that no perceptible change has occurred in ground water quality
over the past 20 years.
Topography. The ground surface is quite flat
immediately adjacent to the present city limits. The
percent.
Site Characterization. Although the city limi
existing lots were not available to the study. The
range of costs for various lot sizes.
within the present community and in the areas
maximum slope in the area is approximately 5
ts enclose an area of about 500 acres, the sizes of
lost/effectiveness analysis, however, considered a
Alternatives and the Screening Process
The two basic alternatives considered for Belevue were: continuing the use of the ST-SAS's
and installing community sewers followed by some form of treatment and surface discharge. On-site
alternatives, other than the ST-SAS's, were not considered for the following reasons:
• Present ST-SAS's have experienced a low failure rate.
• No ground water degradation is notice* ble in wells downstream of the community in
samples taken 20 years apart.
• Population growth projections do not indicate that ground water degradation will be a
future problem.
Ground water depths and soil permeab
lities are suitable for the use of the ST-SAS.
17
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Cost/Effectiveness Analysis
An analysis of the cost/effectiveness of the use of the ST-SAS for the community of Bellevue
is presented in two parts. The first part covers an analysis of total annual costs of a new ST-SAS
compared to the annual cost of collection sewers for various lot sizes. The second covers the total
annual cost of a complete sewerage system composed of collection and trunk sewers and three types
of community treatment systems.
Homeowner Costs. The cost of septic tank-drainfield systems is relatively constant regardless
of lot size, assuming that initially there is sufficient acreage to handle the required system and that
the topography and soil types are suitable. In contrast, community sewerage cost to the home-
owners varies directly with lot size. As the size of lot is reduced and as the proximity of the houses
to one another increases, the overall cost of sewers to the homeowner is reduced, as the cost for the
same length of sewer line is divided among an increased number of homeowners. It is therefore pos-
sible to compare the cost of septic tank-drainfield systems with the varying costs of community
sewerage to determine the size of lot at which it becomes more economical to use a community
waste treatment and disposal system. Nonetheless' comparison in terms of cost alone should not be
the only factor in determining minimum lot size for septic tank systems. Although cost can be a
limiting condition for planning purposes, other factors must be considered as, for example, avail-
ability of a public water supply and public acceptance of septic tanks. If all other factors are equal,
public sewers should not be planned for residential areas if the overall cost is going to be more than
for septic tank systems.
The cost of septic tank systems in Elaine County is presented in table II-5. Installation costs
were obtained from local installers. The overall cost estimate is based on construction of a three-
bedroom home, using Idaho regulations and assuming a percolation rate of 10 min/in. The resulting
design criteria is 165 ft3 per bedroom. The annual costs were computed for a 20-year period at 8'
percent interest. Operational and maintenance costs included the periodic cost of pumping the
tanks and the administrative cost associated with a proposed maintenance district. Operation and
maintenance costs also include an allowance for a maintenance district. If the construction of such a
district is either delayed or ignored, the cost to the homeowner will, of course, be less.
Costs of community sewerage consist of three basic items: construction and maintenance of
collection sewers; construction and maintenance of trunk sewers; and construction, operation, and
maintenance of some type of community waste treatment and disposal system. An estimate of the
cost of collection sewers alone was made in terms of construction costs and assessment formulas, in
two nearby localities in which community sewerage systems had been constructed within the past 5
years. The results of that estimate are shown in figure II-l.
It is apparent from a review of table II-5 and figure II-l that at a 1-acre gross lot size, the
annual cost of an ST-SAS equals the annual cost for local collection sewers alone. In developing
areas, between 25 and 40 percent of the gross lot size is normally used for streets, schools, public
facilities, and small commercial zones. An even smaller lot size is more economically served by sep-
tic tank systems, given the costs of trunk sewers, treatment, and disposal. The cost to the home-
owner for the septic tank systems, however, may not be more than 10 to 25 percent of the actual
cost, because of State and Federal grants. The break-even gross lot size may be as low as 0.25 acre if
expensive forms of treatment and disposal are necessary. In these cases the governing factors on lot
sizes for ST-SAS use will be setback distances and the possible requirement for a replacement drain-
field. An estimate of homeowner costs for conveyance and treatment, excluding the influence of
grant monies, ranged from $60 to $150 per dwelling, depending on the type of treatment. The
lower value was for land application by infiltration-percolation and the higher value was for tertiary
treatment and river discharge.
Community Costs. Costs determined for Bellevue in the study included initial construction
cost, average annual operation and maintenance costs, annualized construction cost, and total
18
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5,000
fe 4,000
8
2 o
O ~ 3,000
§ e
H | 2,000
CO ~0
O
O 1,000
0
Construction cost
-1500
Annual cost
Notes.—Construction cost based on assessment formula used in
city of Ketchum sewerage project. Updated to EPA index 350.
Annual cost based on 8 percent interest and 20-year planning ~
period.
_L
0
0.5
1.0
400
300 O
200 =i
100
1.5
2.0
2.5
3.0
AVERAGE GROSS LOT SIZE, acres
Figure 11-1. Cost of sewerage systems, Bellevue.
Table I \-5.-Estimated construction and maintenance cost for individual disposal systems, Bellevue
, . [I
Septic tank system costs
Initial installation:
Septic tank 1 000 gallons
Drainfield 250 lineal feet
Permit0
Total
Operation and maintenance costs:
Administrative cost of
Septic tank pumping ($80 every 4 years)0 ....
Total
Jollars]
Construction
cost3
370
1,250
20
1,640
1,250
_
Annual
cost
_
.
150b
38b
30
20
238
aAII costs are based on an EPA index of 350.
bBased on 8 percent interest and a 20-year planning period. The replacement drainfield is assumed to be required after 10 years,
and the economic life of the entire septic tank system is assumed to be 40 years.
cBased on information from the County Health District.
annual cost. The annualized construction cost vfas calculated on the basis of a 20-year period and an
interest rate of 6.125 percent. Table II-6 shows
SAS and construction of collection sewers that
cost comparisons of the continued use of the ST-
would include various types of treatment and dis-
posal. In broad terms, use of the ST-S AS is 30 j ercent less expensive in total annual cost than the
least expensive form of community sewerage. This would still hold true even if allowance were
made for the conservative assumption of impler lentation of a maintenance district.
19
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Table \\-Q.-Community sewerage costs, Bellevue
[Thousand dollars]
Waste management option
ST-SAS
Collection sewers, gravity
Collection sewers plus activated sludge
treatment
Collection sewers plus activated sludge plus
removal of nitrogen and phosphorus
Collection sewers plus conveyance plus lagoon
treatment plus disposal by infiltration-
percolation
Construction
cost
1 400a
1 330
2 720
3430
1 910
Annual
construction
cost
1 15
094
20"?
270
144
Average
operation
and
maintenance
cost
Ad
4
R9
87
cc
Total
annual
cost
1RQ
fine
9KR
QK7
9f"IQ
"Includes new ST-SAS and drainfield replacement after 10 years for new homes. For existing dwelling units, only drainfield
replacement cost is included.
Given the previously determined facts that there were no overriding detrimental social or envi-
ronmental impacts, continued use of the ST-SAS was recommended for Bellevue.
WESTBORO
Westboro is a community of 200 persons located in Taylor County in northcentral Wisconsin.
At present, it has no municipal wastewater collection or treatment system, and all buildings in the
community are served by septic tank systems, 80 percent of which were found to be discharging
wastes to the ground surface in 1971. Although a wastewater plan was developed in 1967, prohibitive
costs and lack of available Federal funding have prevented implementation of a community sewerage
system. In the interest of alleviating their sewage disposal problems, the Westboro residents agreed
to cooperate with the Small Scale Waste Management Project (SSWMP) of the University of Wiscon-
sin in an effort to develop an alternative plan that might result in a more cost/effective facility. The
material for the case history is taken from the report of that investigation.4
Physical Characteristics
The Westboro Sanitary District encompasses segments of Silver Creek as it flows southward to
the east of the town center and then turns westward along the southern edge of the community.
The decline of the lumber industry reduced the population from 900 at the turn of the century to
the present 200 residents. It left the community with a cheese factory, a small machine tool com-
pany, and a sawmill to provide local employment. A summary of the physical information reported
by the SSWMP follows:
Climate. No specific climatic information was given in the project report, but Westboro is lo-
cated in an area of Wisconsin that has, on the average, relatively short, mild summers and long, cold
winters.
Soils and Geology. The soils in and around Westboro are primarily deep, well- to somewhat
poorly drained loams and silt loams over sandy glacial till. The populated areas of the community
20
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are usually located on soils judged unsuitable for septic tank systems. Suitable soils can be found
within the city limits, including thick deposits of Well-graded sand in one location. Mucky peat soils
predominate in the southern half of the community.
Ground Water. The report provides no direct information on ground water depths. The exist-
ence of the mucky, peat soils in the southern half of the community, however, indicates near-
surface levels in that area, but ground water levels are apparently much lower in the northern half of
town. Well monitoring since March 1975 has shown 7 of 30 wells sampled to be bacteriologically
unsafe, one of which has also had nitrate concent'ations consistently above the drinking water
standard of 10 mg/1 nitrogen.
Site Characteristics. There are no steep slopes in the community. The central area of Westboro,
known as the Front Street area that includes the pusiness district, is divided into small lots approxi-
mately 50 by 150 feet in size.
Alternatives and Screening Process
As a result of the sanitary survey taken in 1(1)71, the Wisconsin Department of Natural Re-
sources had declared the sewage disposal situation to be a nuisance and a menace to health and com-
fort. It had issued an order to Westboro to construct a community collection and treatment system
or prohibit sewage discharge from private homes into Silver Creek. The initial 1967 study and the
latest study were completed under this order. With respect to the screening process to develop alter-
natives, the SSWMP report revealed the following facts:
• Lot sizes and soils prevent the replacement of most of the failing septic tank systems,
thereby eliminating the choice of alternative.
• The community was divided geographically into five separate areas.
• It was believed that two of the five areas were too sparsely developed for a collection
system. Soils were judged suitable for either a conventional ST-SAS or an ST-Mound
system. Individual systems were therefore recommended as the cost/effective solution.
In two of the remaining three areas, physical
individual systems of some type, but it
offered the greatest advantage because
conditions were also judged suitable for
was decided that a common collection system
of the density of homes.
• A collection system was also considered the best alternative for the fifth area, the central
area that includes the business district and homes with lot sizes too small to permit the
construction of replacement drainfields or other on-site treatment and disposal alterna-
tives.
Several alternatives were to undergo cost/effectiveness analysis to ascertain their ability to
serve the three areas considered worth sewering. Two areas (the Front Street central area and
Joseph's Addition) were combined in each of the alternatives, because of the limited number of
disposal sites available in each separate area. Alternatives for these two areas included using both
pressure and small-diameter gravity sewers to convey septic tank effluent for disposal in a sand bank
east of town along Silver Creek.
Four alternatives were considered for the remaining area (Grossman's Addition).
Pressure collection of septic tank efflue|nt and disposal with the Front Street and Joseph's
Addition areas
21
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Small-diameter gravity sewer collection of septic tank effluent with the following disposal
alternatives:
— Pumping to the Front Street and Joseph's Addition gravity system
— Soil Absorption
— Sand filtration-chlorination and discharge to Silver Creek
Cost/Effectiveness Analysis
The analysis of the cost/effectiveness of the aforementioned conventional gravity sewer alter-
natives and the new alternatives included consideration of total cost at present worth, consideration
of environmental impact, and a determination of system reliability. Cost analyses were based on a
20-year system life and 7 percent interest. Service connection costs were not included in the alter-
natives.
Conventional Alternatives. Costs of the alternatives analyzed in 1967, involving use of conven-
tional gravity sewers, a community treatment plant, and surface water discharge, were updated. The
cost of installing new individual systems in the two sparsely populated areas was added to each of •
the alternatives to permit comparison with the six new alternatives examined by SSWMP. The pres-
ent worth of the two conventional systems is shown in table II-7. The two systems were 17 to 20
percent more costly than the least expensive new alternative analyzed subsequently, and neither
conventional alternative was recommended for implementation.
New Alternatives. The present worth of the six new alternatives was determined and are given in
table II-8. Of the new alternatives, alternative 5 is the least expensive, costing $266,416, or approxi-
mately $3,861 for a household. The cost for each household is significantly less than the cost of
conventional alternatives 1 and 2 ($4,614 and $4,838, respectively).
The environmental impact of new alternative 5 was expected to be minimal. Only nitrogen in
the form of nitrate was expected to leach through the soil to the ground water basin in significant
amounts. Some of the nitrogen was also expected to reach Silver Creek owing to the short distance
between the soil absorption field and the creek.
Table 11-7.— Cost comparison of conventional alternatives, Westboro
[Thousand dollars]
Alternative
1. Conventional gravity sewers plus extended aeration package
plant plus discharge to Silver Creek
2. Conventional gravity sewers plus raw sewage stabilization pond
discharge to Silver Creek
Present worth8
Collection
136.3
136.3
Treatment
170.1
185.5
Individual
systems
12.0
12.0
Total
cost
318.4
333.8
alncludes both capital and operation and maintenance costs.
22
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Table \\-8.-Costcomparison o
[Thousand
f new alternatives, Westboro
dollars]
Alternative
•
1 . Part A: small-diameter gravity sewers to drainfield;
part B: small-diameter gravity sewers to
drainfield
2. Part A: small-diameter gravity sewers to drainfield;
part B: pressure sewers to drainfield
3. Part A: small-diameter gravity sewers to drainfield;
part B: small-diameter gravity sewers to
. drainfield
4. Part A: small-diameter gravity sewers to sand filter;
part B: pressure sewers to drainfield
5. All small-diameter gravity sewers to single drain-
field
6. All pressure sewers to single drainfield
Gr
a
Present worth3
>ssman's
Idition
(part A)
124.5
124.5
148.0
148 0
(c)
(c)
Front St
and Joseph's
addition
(part B)
145.2
185.3
145.2
1853
(c)
(c)
Joint
u
system
269.7
309.8
293.2
333 3
254.4
294.2
Individual
systems
12.0
12.0
12.0
120
12.0
12.0
Total
cost
281.7
321.8
305.2
345 3
266.4
306.2
Includes both capital cost and operation and maintenance cost.
bSum of costs for part A and part B.
clndividual cost not given in report.
Finally, in selecting new alternative 5 the report states:
The reliability of this type of facility has not been established, but its selection is warranted because it is de-
signed from extensive experience with smaller systei ns and its cost and environmental impact are a significant
improvement over the conventional central facilities
Since completion of the project report, decis ions have also been made to serve the sparsely
developed Queenstown and Appaloosa Lane areas
In the Queenstown area, site investigation for possible design of ST-Mound systems showed that
there was insufficient area on the occupied lots to
could not be purchased. In the meantime, the We;
of Westboro with small-diameter gravity sewers.
construct the intended system, and adjacent land
tboro Sanitary District decided that it would also
be beneficial to extend small-diameter gravity sewers to, and slightly beyond, the Appaloosa Lane
area. At present, therefore, it appears that the entire community will be served by a sewerage sys-
tem composed of individual septic tanks, small-diameter gravity sewers, and a community SAS.
FOUNT
A.IN RUN
The city of Fountain Run is located in Monroe County, in southcentral Ky. The planning area
for the 201 Study is the area served by the Fountain Run Water District, including the city of Foun-
tain Run and a portion of Monroe County. The study area is without a public sewerage system at
present, and all wastewater is disposed through eitner ST-SAS's or privies. Of the existing ST-SAS
units, approximately 20 percent are located on soils with permeabilities of less than 0.5 in/h. More-
over, an estimated 30 percent of the systems are, £ t least, producing surfacing effluent during the
winter months. All material for the case history is
taken from the facilities plan for the area.5
23
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Physical Characteristics
The study planning area covers about 2,240 acres in the western portion of Monroe County.
The population of the county and the city of Fountain Run declined significantly during the
1960's, leaving approximately 320 people in the city and some 440 in the water district. Detailed
physical characteristics follow.
Climate. The climate in the Fountain Run planning area is temperate. Freezing temperatures
occur on fewer than 85 days annually, and there are approximately 50 days with maximum tem-
peratures above 90° F. The average annual snowfall and total precipitation depths are 10 inches and
50 inches, respectively. Estimated annual evaporation is 40 inches.
Soils and Geology. Bedrock in the study area is limestone, interbedded with chert and dolo-
mite. The soil is described as predominantly deep, well-drained, claylike, and loamy. According to
information provided by the Soil Conservation Service, a substantial portion of the area within the
city limits has no limitations on subsurface disposal systems. As noted earlier, however, about 20
percent of the existing systems are located on soils with permeabilities of less than 0.5 in/h.
Ground Water. Limited information was available to the facilities plan investigators. One well
located south of the planning area is reported to have a depth of 39 feet. The report contains no
information with respect to ground water quality. No public water supplies use ground water
sources, however, as they are inadequate, from a hydrauh'c standpoint, to sustain the withdrawal
rates required for domestic consumption.
Site Characteristics. The planning area lies in the upper reaches of two small watersheds and
contains gently rolling hills and moderate slopes having elevations from 700 to 850 feet. Lot sizes
are usually over 0.75 acre. The smallest lot in Fountain Run is approximately 12,000 ft2, or slightly
larger than one-quarter acre.
Alternatives and the Screening Process
A separate, explicit screening process is not presented in the facilities plan for Fountain Run.
The following facts form the basis for analysis of a limited set of wastewater management alterna-
tives:
• Optimum operation of existing individual disposal systems was considered, but it was
judged impractical to try to upgrade them to the level of current septic tank system
technology.
• Implementation of any regional solution was also quickly rejected as the closest town, in
a neighboring county, is 12 miles away, and an estimate of the capital cost of an inter-
ceptor system to deliver Fountain Run's sewage to the neighboring town exceeded $1
million and was nine times more expensive than any local alternative.
• A previous engineering report on sewerage for Fountain Run had been prepared using
conventional gravity sewers with oxidation pond treatment. The data from that study
were available to be updated as one alternative.
» A substantial portion of the soils within and adjacent to the city limits is suitable for dis-
posal by soil absorption.
As a consequence of the preceding factors, four alternatives were considered. They are:
24
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A.
B.
A conventional gravity sewer collection system, with one of two types of treatment: (1) a
package, complete-mix, activated sludge unit followed by soil infiltration-percolation and
(2) an oxidation lagoon with infiltration-percolation disposal
Community-wide collection by an effluent sewer system consisting of individual septic
tanks with siphons or pumps and small-diameter plastic pipelines carrying partially
treated sewage by pressure and gravity;
infiltration-percolation
treatment in an oxidation pond and disposal by
C. The collection of septic tank effluent for clusters of houses in small-diameter pressure and
gravity sewers; disposal in SAS's in suitable soils; individual septic-tank systems used
where appropriate
D. Completely individual on-site
systems forced to rely on nonstandard J
disposal throughout the community, with 20 percent of the
j ystems because of soil conditions
Cost/Effectiveness Analysis
An analysis of the cost/effectiveness of alternatives
District included detailed cost estimates of collection
assessment. All cost analyses were put in terms of
design period and an interest rate of 6.125 percen
estimated and subtracted from total present wortrji
to determine net present worth.
for sewerage in the Fountain Run Water
and treatment systems and an environmental
present worth for comparison, using a 20-year
;. The salvage value of all capital expenditures was
(capital plus operation and maintenance costs)
Alternative A. The collection system for this alternative included over 20,000 feet of 8-inch
line, 1,800 feet of 6-inch line, a pumping station, and 600 feet of force main. The total construction
cost for the collection system was estimated to be $339,600, with an estimated annual expenditure
of $9,000 for operation and maintenance. Net present worth of the collection system after subtract-
ing salvage value, but including operation and maintenance costs, was determined to be $390,100.
Two methods of treatment were examined and selected on the basis of the consultant's past experi-
ence with treatment systems for small communities. Net present worth of the 2-acre oxidation
pond, including operation and maintenance costs, was $81,600, and that of the package activated
sludge unit was $89,500. Three types of disposal s|ystems were analyzed for alternative A: an inter-
ipray irrigation, and infiltration-percolation. In-
mittent sand filter system and effluent discharge,
eluding operation and maintenance costs, net pre
$61,100, $74,900, and $53,900, respectively.
disposal method used in alternatives A-l and A-2
natives is also given in table II-9.
;nt worth of the three disposal systems came to
Ltration-percolation was therefore chosen as the
[shown in table II-9). Present worth for both alter-
Alternative B. The collection system for alternative B included about 20,000 feet of 2- to 4-
inch plastic pipe without manholes. Some would be pressure lines, but most were designed to accept
gravity flow. Also included in the collection system were some 3,800 feet of 8-inch gravity line,
septic tanks with siphons or pumps, five larger main-line pumps, and one pumping station. Opera-
ting costs included in the net present worth of the collection system were pump operation and
maintenance, septic tank pumping on a 5-year cycle, and flushing of small-diameter lines as needed.
Net present worth of the alternative B collection system alone, including operation and mainten-
ance costs, was estimated to be $246,900. Community treatment and disposal for the alternative B
system was the same oxidation pond and infiltrati
>n-percolation basin combination used in alterna-
tive A-2. The component costs of alternative B are shown in table II-9.
Alternative C. Design criteria for the SAS's uped in alternative C included an assumed average
household wastewater flow of 200 gal/d and an application rate of 0.33 gal/ft2 /d (approximately
400 ft2 per bedroom) to the trench sidewalls in each of two half-systems (600 ft2 per half-system)
25
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Table 11-9.—Cost comparisons of alternatives. Fountain Run
[Thousand dollars]
Alternative
A-1
A-2
B
c
D
Present worth
Construction cost3
Collection
287.9
287.9
176.9
Treatment
and disposal
47.9
86.1
86.1
Combined
collection,
treatment,
and disposal
335.8
374.0
263.0
228.2
206.4
Operation
and,
maintenance
197.8
151.6
119.4
74.5
61.9
Total
cost
533.6
525.6
382.4
302.7
268.3
Includes initial and 10-year expansion costs, less salvage value.
to be used in alternate years. Public management of all on-site and community wastewater facilities
was considered critical to the alternative. Homes were grouped in several patterns before the final
selection was made. The object was to achieve an optimum mix that would provide disposal to the
most suitable soils by means of a low cost, simple operation. It should also be able to accommodate
future growth. The resulting design included 22 individual on-site systems and 22 systems with two
or more households orbusinesses ,using_a_common disposal field. The 22 community systems called
for construction of SSSieejtof 8-inch gravity sew.er} 10,400 feet of 4rinch gravity sewer for septic
tank effluent, and 1,200 feet of^2^jmd_&-racrrfiqes for septic tank effluent. Operation and mainten-
ance costs were assumed to include pump operation and maintenance, line flushing and repair, ser-
vicing septic tanks on a regular schedule, inspection of disposal field condition, repair and mowing
of disposal fields, and periodic alteration of flow in the fields. The costs were estimated to total
$6,110 per year. Components of the total present worth of $302,700 for the alternative are shown
in table II-9.
Alternative D. Because on-site disposal was being used with some degree of success in the area,
the consultant considered community management of individual on-site systems as an alternative.
The cost analysis used construction costs of $1,200 for standard ST-SAS units and 50 percent more,
or $1,800 per unit, for construction of nonstandard systems for the existing 20 percent of the sys-
tems located in soils described as having severe limitations for subsurface disposal. Total present
worth of alternative D was determined to be about $268,300 as shown in table II-9.
Evaluation of Alternatives. The on-site disposal alternative (D) not only had the lowest total
present worth of all alternatives evaluated, but was also given the highest rating with respect to envi-
ronmental impact. The report also states, however, that the difference ih estimated cost between
alternatives C and D was probably less than the level of precision used in estimating alternative D. In
addition, there was no significant difference in the environmental rating of any of the five alterna-
tives. From the standpoint of implementation, alternative D was not recommended, because of un-
certainty of the actual costs of systems required in areas with poor soils. Public opinion, including
that of the Water District Commissioners, favored alternative C. Considering all factors, alternative
C, community subsurface disposal, was selected as the recommended plan, and a user charge of
$7.10 per month was estimated necessary to support the wastewater services provided by the selec-
ted plan.
26
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EAST RYEGATE
The community of East Ryegate, Vt., is one of three villages that make up the town of Rye-
gate in the southeastern corner of Caledonia County, in the Connecticut River Valley. At the time
the facilities plan for East Ryegate was being conducted, a small combined collection sewer system
served the estimated 140 persons in the communitjy and discharged raw sewage into the Connecticut
River and into a small drainage channel. The NPDES permit compliance schedule for Fire District
No. 2 of East Ryegate required that a subsurface disposal system be in operation by June 1,1976.
The report that serves as the basis of the case history is a revision of an August 1972 report.6
Physical Characteristics
Soils, ground water, and site characteristics o
not described in the facilities plan, as it did not
the study area are described below. Climate was
on any of the alternatives evaluated.
bear
Soils. Information taken from soil borings made during the investigation indicated that the
soils beneath the village are composed of sandy loam, coarse sand, and silty gray clay. The clay layer
appears to exist beneath the entire study area and varies from 2 feet below the surface in the west-
ern corner of the village to 12 feet in the village center. Percolation rates in most soil borings were
less than 10 min/in; many were on the order of 1 min/in.
Ground Water. Ground water is found below
the impervious clay layer throughout the study
area. Test pits dug south of the community in OctDber, 1973 showed ground water levels varying
from a minimum depth of 4.5 feet to over 10 feet
The report contains no information relative to
ground water quality. It can be assumed that present quality is adequate for domestic uses, as the
community water supply well is located in the village center, and it supplies untreated water for
domestic use.
Site Characteristics. Terrain throughout the
elevations ranging from about 470 to 490 feet abo|ve
described in the report, it does state that the 40 d
settlement and that many of the lots do not have
drainfield.
village of East Ryegate is quite flat, with ground
sea level. Although no specific lot sizes are
veilings in the study area are located in a dense
mough open area to accommodate an 1,800-ft2
Alternatives and Screening Process
The investigation selected four basic alternatives for study, one with five variations. The alter-
natives were as follows:
I. No action
II. Treatment and water reuse
III. Municipal extended aeration
IV. Septic tank and subsurface disposal
a. individual private systems
b. joint private systems
c. individual-municipal system
27
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d. municipal system-gravity flow
e. municipal system-force main
The screening process for the alternatives involved analyzing each from the standpoint of sev-
eral questions.
• Does the alternative comply with State regulations and Federal guidelines?
• Does the alternative offer the best treatment process for the costs involved?
• Is the alternative capable of meeting the implementation schedule for the district as set
forth by the NPDES permit?
Alternatives I and II were both eliminated in the initial screening phase, as alternative I does
not comply with either State or Federal requirements and alternative II does not comply with the
laws of the State of Vermont.
Cost/Effectiveness Analysis
Following elimination of alternatives I and II, those remaining were examined. Present worth
analyses were based on the use of a 20-year design life and 7 percent interest.
Alternative III. This plan, proposed initially in a consulting engineer's report in 1970, would
use an addition to the existing collection system to convey the community's sewage to a package
extended aeration plant. It has two advantages: it would end the pollution of surface streams and it
proposes a feasible treatment method, but in contrast, it involves high operation and maintenance
costs and requires more power than any other alternative. Furthermore, the costs include extensive
use of the existing collection system that the State Department of Water Resources subsequently
determined to be inadequate on the basis of an infiltrative inflow analysis. Vermont's cost/effective
solution was construction of a new collection system for sanitary sewage only and retention of the
old system as a storm sewer. The actual construction costs of the collection system for the alterna-
tive are higher, therefore, than the $96,000 included in the total capital cost in table 11-10.
Alternative IVa. Installation of private septic tank systems for each individual residence in East
Eyegate assumes that every residence can be served by such a system. As a practical matter, the
Tabl e 11 -10.—Cost comparison of sewerage alternatives for East Ryegate
[Dollars]
Alternative
III. Municipal extended aeration
IVa. Individual subsurface systems
IVb. Joint private systems
IVc. Individual-municipal system
IVd. Municipal system-gravity flow
IVe. Municipal system-force main
Total capital
cost
253 200
33000
38 500
1 29 800
312 000
271 700
Average annual
operation and
maintenance cost
6 100
900
900
2 000
1 600
2 000
Present worth3
302 900
42 500
48000
145 300
310400
274 300
"Present worth of salvage value deducted for all alternatives using community facilities.
28
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report lists several obstacles to that assumption: th
village overlie a clay layer less than 2 feet from the
3 soils fronting on one of the four streets in the
ground surface; only a few dwellings have as
much as 1,800 ft2 of open area in which to construct an ST-SAS; and if systems could be placed on
all lots, the leachate from those in the central part Df the village would flow toward the public water
supply well. The costs shown in table 11-10 assume
signed ST-SAS at a cost of $1,100.
that each residence can install a properly de-
Alternative IVb. In an attempt to improve the possibility of individual disposal, alternative IVb
was developed. It proposes the combining of wastewater from several dwellings in small collection
systems with disposal to lots that have suitable soils and size to accommodate the combined flow. It
would therefore comply with State regulations. The disadvantages are that: there may not be suffi-
cient suitable lots to serve all dwellings, and the issue of ownership and user's rights may be raised
when neighbors start discharging wastes to one another's property. The difference in capital cost in
table 11-10 between the two alternatives, IVa and IVb, is attributed to engineering, land, and ad-
ministrative costs.
Alternative IVc. An attempt to provide a community wide system for those dwellings that can-
not be served by Alternatives IVa or IVb prompted Alternative IVc. The residences that could use
subsurface disposal would not be permitted to connect to the municipal system under this alterna-
tive. The community system would be designed to collect wastewater flows into an interceptor for
conveyance by either gravity or force main to a municipally owned and operated ST-SAS. The time
required for inspection of lots and for notifying owners of the decision that they are to construct an
individual system or connect to the community system might exceed the time allowed in the
NPDES permit compliance schedule. Moreover, the cost of the community system could be prohibi-
tive for the small number of owners that would connect to it initially. Of the total capital cost
shown in table 11-10, about $83,000 is for collection and disposal, $12,500 for treatment, and
$34,000 for engineering, land, and administrative costs.
Alternative IVd. Under this alternative, a low-
subsurface disposal field for the entire community.
would permit installation of a conventional gravity
have to be filled with approximately 17,000 yd3 ol
obtained for this plan, because of the proposed use
permit general use of the fill system. Capital costs i
ponents: collection and disposal system—$236,000
gineering, land, and administrative costs—$49,600.
[ying area north of the village would serve as a
Although use of the proposed disposal site
collection system, the disposal area itself would
imported soil. State approval would have to be
of the fill system. At present, Vermont does not
ih table 11-10 are composed of the following com-
; treatment system (septic tanks)—$26,400; en-
Alternative IVe. In this alternative, the collection system would consist of conventional gravity
sewers conveying all wastewater to a pumping station in the northeast corner of the village, and a
force main would operate from the pumping station to a municipal ST-SAS located south of the
village. Soils at the proposed SAS site appear suitable. As noted in the facility plan, the cost of the
system is nominal with Federal aid but prohibitive for the district without it. The total capital cost
for the alternative is $271,700: $195,000 for the collection and disposal systems, $26,400 for the
treatment system, and $49,600 for engineering, land, and administrative costs.
Evaluation of Alternatives. The results of the evaluation of the alternatives were as follows:
» Alternatives I and II were not recommended for the reasons given earlier.
» Alternative III was not recommended because of its high operation costs and power re-
quirements, and because, as presented, it
collection system.
Alternatives IVa and IVb were not recommended because data on soils indicate that sub-
surface disposal may not be feasible thro
29
would use a portion of the existing inadequate
ughout much of the residential area.
-------
Alternative IVc was not recommended because of the high annual cost, which would have
to be paid by the few users of the community portion of the system.
Alternative IVd was not recommended because of poor soil and high ground water at the
proposed disposal site, and because the extensive modifications required to make the site
suitable may not be acceptable to the State.
Alternative IVe is therefore recommended as the most cost/effective method of allevi-
ating existing stream pollution.
REFERENCES
1 Department of Public Works, Douglas County, Oreg., "Glide-Idleyld Park Sewerage Study,
Douglas County, Oregon," Dec. 1975.
2Doviglas County Engineer's Office, "Pressure Sewer'Systems," Roseburg, Oreg., May 1974.
3 Brown and Caldwell, "Wastewater Facilities Plan Project Report, Elaine County," A report
prepared for Elaine County, Idaho, Nov. 1976.
4R. J. Otis and D. E. Stewart, "Alternative Wastewater Facilities for Small Unsewered Com-
munities in Rural America," A report of the Small Scale Waste Management Project, University of
Wisconsin, Madison, July 1976.
5Parrott, Ely, and Hurt Consulting Engineers, Inc., "Sewerage Facilities Plan, Fountain Run,
Kentucky," A report prepared for the Fountain Run Water District, July 1976.
6 Dufresne-Henry Engineering Corporation, "Facilities Planning Report on Wastewater Collec-
tion and Treatment," A report prepared for Fire District No. 2, Ryegate, Vt., Mar. 1975.
30
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METRIC CONVI
Recommended Units
Description
Length
Area
Volume
Mass
Force
Moment or
torque
Flow (volumetric)
Unit
meter
kilometer
millimeter
micrometer or
micron
square meter
square kilometer
square millimeter
hectare
cubic meter
litre
kilogram
gram
milligram
tonne
newton
newton meter
cubic meter
per second
liter per second
Symbol
m
km
mm
•ftm or/i
m2
km2
mm2
ha
m3
1
kg
g
.mg
t
N
N-m
m3/s
l/s
Comments
Basic SI unit
The hectare (10,000
m2) is a recognized
multiple unit and will
remain in interna-
tional use.
Basic SI unit
1 tonne = 1,000 kg
The newton is that
force that produces
an acceleration of
1 m/s2 in a mass
of 1 kg.
The meter is mea-
sured perpendicular
to the line of action
of the force N.
Not a joule.
Customary
Equivalents*
39.37m =3.281 ft =
1.094 yd
0.6214 mi
0.03937 in
3.937 X lfl-5in=1 X 104^
1Q.76sqft=U96sqyd
0.3861 sq mi = 247.1 acres
0.001550 sq in
2.471 acres
35.31 cuft=1.308cuyd
1. 057 qt = 0.2642 gal =
0.8107 X104 acre ft
2.205 Ib
0.03527 oz = 15.43 gr
0.01 543 gr
0.9842 ton (long) •
1.102 ton (short)
0.2248 Ib
= 7.233 poundals
0.7375 Ib-ft
23.73 poundil-ft
15.850 gjun =
2,119cfm
15.85 gpm
Application of Units
Description
Precipitation,
run-off.
evaporation
Flow
Discharges or
abstractions,
rvields
Usage of water
Unit
millimeter
-
cubic meter
per second
liter per second
cubic meter
per day
cubic meter
per year
liter per person
per day
•Miles are U.S. statute, qt and gal are U.S
Symbol
mm
m3/s
l/s
m3/d
m3/year
I/person/
day
Comments
For meteorological
purposes, it may be
convenient to meas:
sure precipitation in
terms of mass/unit
area (kg/m2).
1 mm of rain =
1kg/m2
1 l/s = 86.4 m3/d
Customary
Equivalents*
35.31 cfs
15.85 gpm
0.1835 gpm
264.2 gal/year
0.2642 gcpd
liquid, and oz and Ib are avoirdupois.
IRSION TABLES
Recommended Units
Description
Velocity
linear
angular
„
Viscosity
Pressure or
stress
Temperature
Work, energy,
quantity of heat
Power
Unit
meter per
second
millimeter
per second
kilometers
per second
radians per
second
pascal second
cent! poise
newton per
square meter
or pascal
kilo newton per
square meter
or kilo pascal
bar
Celsius (centigrade)
Kelvin (abs.)
joule
kilojoule
watt
kilowatt
joule per second
Symbol
m/s
mm/s
km/s
rad/s
Pa-s
2
N/m2
or
Pa
kN/m2
or
kPa
bar
°C
°K
J
kj
W
kW
J/s
Comments
1 joule - 1 N-m
where meters are
measured along
the line of action
of force N.
1 watt = 1 J/s
Customary
Equivalents*
3.281 fps
0.003231 fps
2,237 mph
9.549 rpm
0.6722 poundal(s)/sq ft
1.450 X10'7Reyn(p)
0.000 1450 Ib/iq in
0.14507 Ib/sq in
14.50 Ib/sq in
(°F-32)/1.8
°C + 273.2
2.778 X 10'7
kw-hr =
3.725 X lO'7
hp-hi = 0.7376
ft-tb = 9.478 X
10"4 Btu
2.778 X IQ-^kw-hr
44.25 ft-lbs/min
1.341 hp
3.412 Btu/hr
Application of Units
Description
Density
Concentration
BOD loading
Hydraulic load
per unit area,
e.g., filtration
rates
Air supply
Optical units
Unit
kilogram per
cubic meter
milligram per
liter (water)
kilogram per
cubic meter
per day
cubic meter
per square meter
per day
cubic meter or
liter of free air
per second
lumen per
square meter
Symbol
kg/m3
mg/l
kg/m3/d
m3/m2/d
m3/s
l/s
lumen/m2
Comments
The density of water
under standard
conditions is 1,000
kg/m3 or 1,000 a/I
or 1 g/ml.
If this is converted
toavelocity.it
should be expressed
in mm/s (lmm/s^
86.4 m3/m2/day).
Customary
Equivalents*
0.06242 Ib/cu ft
Ippnt
0.06242 Ib/cu ft/day
3.281 cuft/sq ft/day
0.09294 ft candle/sq ft
AU.S. GOVERNMENT PRINTING OFFICE: 1977—757 - 140 /660Z
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